1. Field of the Invention
The invention relates to an adjustable lens mount for a strip lens, in particular in the form of a long, thin cylindrical lens, as used in scan objective lenses in laser material processing and in the printing industry.
2. Description of the Background Art
The strip lens generally forms the last optical imaging element within an optical arrangement, which focuses the laser beam that passes over the strip lens in a scanning fashion in the direction of the longitudinal extent thereof (scan direction) in an image plane, in which the workpiece to be processed is arranged.
The scan line described by the focus on the workpiece theoretically is a straight line in this case; however, in practice, it deviates from an ideal straight line in the direction of the relative motion between the scan line and the workpiece (cross-scan direction), perpendicular to the scan direction, as a result of tolerances of the components involved in the imaging. In order to keep these deviations within a tolerance limit, it is known to deform the strip lens over the longitudinal extent thereof perpendicular to the optical axis thereof by applying forces at points and thereby linearize the scan line.
Compared to conventional rotationally symmetric lenses, a cylindrical lens is distinguished in term of its design by virtue of the fact that it has an unchanging cross section perpendicular to the longitudinal extent thereof over the whole length thereof and therefore has a constant thickness (extent in the direction of the optical axis). Provided that it is comparatively long and thin, this peculiarity makes it predestined to manipulate the beam imaging in order to linearize the scan line described by the focus by an adjustment via a targeted local deformation in the sub-micrometer range which can be effected with an equally long travel at each point along the length.
In order to provide mechanical stability to a long and thin strip lens, it is conventional for the strip lens to be cohesively applied to a support strip along a joining area, even before the final treatment of its optically active surface. The support strip then remains permanently connected to the strip lens.
In order to enable a deformability of the strip lens, the support strip must be correspondingly deformable with the available adjustment forces or adjustment paths; this is achieved by selecting a flexural strength of the support strip optimized for this, by the choice of material with a suitable Young's modulus and a geometric moment of inertia of the support strip correlated thereto, which is determined by the dimensions thereof, more particularly the thickness.
In accordance with the conventional art, such a support strip is designed to be wider than the required joining area is wide, by means of which joining area the strip lens is fixedly connected to the support strip, in order to provide a sufficiently wide assembly surface on the side opposite to the joining area, on which assembly surface a multiplicity of set screws can engage along the longitudinal extent of the support strip in order to affix the latter in adjustable fashion with respect to a rigid mounting plate.
FIG. 1 illustrates a lens mount with strip lens, as known from the prior art. What is shown is a perspective view with a scale of 1:2 and two sectional illustrations (not to scale).
The lens mount essentially has an elongate support strip 1 with a joining area on which a strip lens 5 can be applied over the whole length thereof and a rigid mounting plate 2, which is provided on the free side of the support strip 1 lying opposite to the joining area. The mounting plate 2 is slightly longer than the support strip 1 and, along the length thereof, has a row of alternately arranged recessed through holes 3.1 and end-to-end threaded bores 3.2. At the ends, the support strip 1 and the mounting plate 2 are assembled at a predetermined adjustment spacing from one another on lateral holders 6, by means of which the lens mount can be attached to a reference surface 10, which is for example provided on a housing of a scanning objective lens.
First set screws 4.1, preferably cylinder head screws, are inserted into the through holes 3.1 and engage into provided threaded drill holes (referred to below as bores 8 provided with a thread to facilitate a distinction) at the free outer surface of the support strip 1. Differentiated tightening of individual first set screws 4.1, which can thereby be adjusted by a differentiated travel, renders it possible locally to pull the support strip 1 toward the mounting plate 2 to a greater or lesser extent.
Second set screws 4.2, preferably set screws with ball terminals, are inserted into the end-to-end threaded bores 3.2 and these butt against the free outer surface of the support strip 1. Differentiated tightening of individual second set screws 4.2 renders it possible locally to push the support strip 1 away from the mounting plate 2 to a greater or lesser extent.
By means of targeted manipulation of the first and second set screws 4.1, 4.2, it is possible to deform the support strip 1, and hence the strip lens 5 fixedly connected to the support strip 1, in a wave-shaped fashion in the sub-micrometer range in the cross-scan direction (CSR).
A disadvantage of the above-described lens mount is the installation space required for this directly adjacent to the strip lens 5. In the illustrated section A-A, it is clearly possible to see that the support strip 1 clearly extends beyond the thickness of the strip lens 5 in the direction of the optical axis, which is the same as the cross-scan direction (CSR). As a result, it is not possible to arrange a further optical or mechanical component in this region.
As a result of the usually very short focal lengths of cylindrical lenses, there often is the need to arrange further optical and mechanical components in the vicinity of the cylindrical lens embodied as strip lens 5, which is why it is disadvantageous if the installation space required for the lens mount, which directly adjoins the strip lens 5, extends beyond the thickness of the strip lens 5.
Moreover, the support strip 1 can undesirably restrict the beam path.
In order to ensure an adjustment of the strip lens 5 after the lens mount has been installed in an optical arrangement, the mechanical connection between the mounting plate 2 and a reference surface 10 can only be brought about via lateral holders 6 in order to enable access to the set screws 4.1, 4.2. Such an attachment assumes particularly high flexural strength of the mounting plate 2.